Apparatus and method for encoding/decoding images for intra-prediction

ABSTRACT

A method of decoding an image includes the steps of restoring a residual value by performing inverse quantization and inverse transform on the residual value by entropy decoding a received bit stream, generating a prediction unit by performing intra prediction selectively using one of a plurality of prediction modes on a prediction unit split by conducting at least one of asymmetric partitioning and geometrical partitioning, and restoring an image by adding the residual value to the prediction unit. It may be possible to enhance encoding efficiency of high-resolution images having a resolution of HD or higher by performing intra prediction on the asymmetric partitioning and/or geometrical partitioning.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/808,076 filed on Jan. 1, 2013, which is the National Phase ofPCT/KR2011/004892 filed on Jul. 4, 2011, which claims priority under 35U.S.C. 119(a) to Korean Patent Application No. 10-2010-0064009 filed onJul. 2, 2010 in the Korean Intellectual Property Office (KIPO), all ofwhich are hereby expressly incorporated by reference into the presentapplication.

BACKGROUND

1. Technical Field

The present invention is directed to encoding and decoding images, andmore specifically to an apparatuses and methods for encoding/decodingimages that may be applied to intra prediction.

2. Description of the Related Art

In general image compression methods, one picture is separated intomultiple blocks each having a predetermined size. Inter-prediction andintra-prediction technologies are used to remove redundancy betweenpictures so as to increase compression efficiency.

The method of encoding images using intra-prediction predicts pixelvalues based on pixel correlation between blocks from pixel values inthe blocks surrounding a current block, which have been already encoded,such as an upper block, a left block, an upper and left block, and anupper and right block in a current frame (or picture), and transmitstheir prediction errors.

In the intra-prediction encoding, among several prediction directions(horizontal, vertical, diagonal, or average, etc.), an optimalprediction mode (prediction direction) is selected to be suited forcharacteristics of an image to be encoded.

In the existing H.264/AVC standards, in the case that theintra-prediction encoding applies to a 4×4 pixel unit block, among nineprediction modes (prediction modes 0 to 8), one most appropriateprediction mode is selected every 4×4 pixel blocks, and the selectedprediction mode (prediction direction) is encoded on a per-4×4 pixelblock basis. Further, in the case that the intra-prediction encodingapplies to a 16×16 pixel unit block, among four prediction modes(vertical prediction, horizontal prediction, average prediction, andplanar prediction), one most appropriate prediction mode is selectedevery 16×16 pixel blocks, and the selected prediction mode (predictiondirection) is encoded on a per-16×16 pixel block basis.

In the existing intra-prediction encoding, a predetermined number ofprediction directions are predefined only for M×M square-typesymmetrical pixel blocks (M=4, 8, or 16) to perform the intra-predictionencoding. That is, conventionally, M×M-size symmetrical partitioningonly is applied for intra-prediction encoding so that a square-typesymmetrical block is used as a basic unit for the intra-predictionencoding.

SUMMARY

It is required a method of increasing coding efficiency because thereare limits for increasing coding efficiency when intra prediction isperformed using only the conventional symmetric pixel blocks.

Especially, it is required a method of increasing coding efficiencybecause there are limits for increasing coding efficiency when intraprediction is performed on high-resolution image having a resolution ofan HD (High Definition) or higher using only symmetric pixel blocks.

A first object of the present invention is to provide an intraprediction encoding method and apparatus that may be applicable to ahigh-resolution image having a resolution of an HD (High Definition) orhigher.

A second object of the present invention is to provide an intraprediction decoding method and apparatus that may be applicable to ahigh-resolution image having a HD (High Definition) or higher.

To achieve the above-described first object of the present invention,according to an aspect of the present invention, a method of encoding animage includes the steps of performing intra-prediction encoding byselectively using one of a plurality of prediction modes on a predictionunit which is split by applying at least one of asymmetric partitioningand geometrical partitioning to an input image so as toprediction-encode the input image and performing transform,quantization, and entropy encoding on a residue which is a differencebetween a prediction unit predicted by the intra prediction and acurrent prediction unit. A pixel value in the asymmetrically partitionedprediction unit may be predicted by using a pixel value in a blockencoded earlier than the prediction unit along one of a verticaldirection, a horizontal direction, an average value prediction, adiagonal down-right direction, and a diagonal down-left direction.

To achieve the above-described second object of the present invention,according to an aspect of the present invention, a method of decoding animage includes the steps of restoring a residue by entropy-decoding areceived bit stream and by performing inverse quantization and inversetransform on the residue, generating a prediction unit by performingintra-prediction encoding that selectively uses one of a plurality ofprediction modes on a prediction unit which is split by applying atleast one of asymmetric partitioning and geometrical partitioning, andrestoring the image by adding the residue to the prediction.

A pixel value in the asymmetrically partitioned prediction unit may bepredicted by using a pixel value in a block encoded earlier than theprediction unit along one of a vertical direction, a horizontaldirection, an average value prediction, a diagonal down-right direction,and a diagonal down-left direction. The pixel value in theasymmetrically partitioned prediction unit may be predicted by using thepixel value in the block encoded earlier than the prediction unit alonglines formed at the same predetermined angle all over the entiredirection within 360°. The pixel value in the asymmetrically partitionedprediction unit may be subjected to intra prediction along a line withan angle corresponding to a slope with dx along the horizontal directionand dy along the vertical direction based on information on dx and dydefining the slope. A predicted pixel value of a pixel positioned at arightmost and lowermost end of the prediction unit may be obtained usingvertically and/or horizontally directional corresponding pixel values inleft side block and upper end block encoded earlier than the predictionunit. The pixel value of the pixel positioned at the rightmost andlowermost end of the prediction unit may be obtained by performinglinear interpolation using vertically and/or horizontally directionalcorresponding pixel values in the left side block and upper end blockencoded earlier than the prediction unit and vertically and/orhorizontally directional corresponding internal pixel value in theprediction unit. A predicted pixel value of a pixel positioned at arightmost and lowermost end of a current prediction unit of an Nthpicture may be obtained by obtaining an average value or performinglinear interpolation using vertically and/or horizontally directionalpixel values in previously encoded left side block and upper end blockwhich are positioned adjacent to the current prediction unit andvertically and/or horizontally directional corresponding pixel values inthe previously encoded left side block and upper end block positionedadjacent to a corresponding prediction unit of an N−1th picture.

To achieve the above-described second object of the present invention,according to another aspect of the present invention, an apparatus fordecoding an image includes an inverse-transform unit configured toreconstruct a residue by entropy-decoding a received bit stream and byperforming inverse quantization and inverse transform on the residue, anintra predicting unit configured to generate a prediction unit byperforming intra-prediction encoding that selectively uses one of aplurality of prediction modes on a prediction unit which is split byapplying at least one of asymmetric partitioning and geometricalpartitioning, and an adder configured to reconstruct the image by addingthe residue to the prediction.

According to the above-described intra-prediction encoding/decodingmethods and apparatuses, the intra-prediction encoding/decoding methodsand apparatuses can enhance encoding efficiency for high-resolutionimages having an HD or ultra HD resolution by applying intra-predictionencoding/decoding to pixels blocks having an asymmetrical shape or anygeometrical shape with a size of M×N.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating a recursive coding unitstructure according to one example embodiment of the present invention.

FIGS. 2 to 5 are conceptual views illustrating an asymmetricpartitioning method according to one example embodiment of the presentinvention.

FIG. 6 is a conceptual view illustrating an intra-prediction encodingmethod using an asymmetrical pixel block according to one exampleembodiment of the present invention.

FIGS. 7 to 9 are conceptual views illustrating an intra-predictionencoding method using an asymmetrical pixel block according to anotherexample embodiment of the present invention.

FIG. 10 is a conceptual view illustrating an intra-prediction encodingmethod based on planar prediction according to another exampleembodiment of the present invention.

FIG. 11 is a conceptual view illustrating an intra-prediction encodingmethod based on planar prediction according to another exampleembodiment of the present invention.

FIG. 12 is a conceptual view illustrating a geometrical partitioningprocess according to another example embodiment of the presentinvention.

FIG. 13 is a block diagram illustrating a configuration of an imageencoding apparatus performing intra-prediction encoding according to oneexample embodiment of the present invention.

FIG. 14 is a flowchart illustrating an image encoding method appliedwith intra-prediction encoding according to one example embodiment ofthe present invention.

FIG. 15 is a block diagram illustrating a configuration of an imagedecoding apparatus according to one example embodiment of the presentinvention.

FIG. 16 is a flowchart illustrating an image decoding method accordingto one example embodiment of the present invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE PRESENT INVENTION

Various modifications may be made to the present invention and thepresent invention may have a number of embodiments. Specific embodimentsare described in detail with reference to the drawings.

However, the present invention is not limited to specific embodiments,and it should be understood that the present invention includes allmodifications, equivalents, or replacements that are included in thespirit and technical scope of the present invention.

The terms “first” and “second” may be used to describe variouscomponents, but the components are not limited thereto. These terms areused only to distinguish one component from another. For example, thefirst component may be also named the second component, and the secondcomponent may be similarly named the first component. The term “and/or”includes a combination of a plurality of related items as describedherein or any one of the plurality of related items.

When a component is “connected” or “coupled” to another component, thecomponent may be directly connected or coupled to the other component.In contrast, when a component is directly connected or coupled toanother component, no component intervenes.

The terms used herein are given to describe the embodiments but notintended to limit the present invention. A singular term includes aplural term unless otherwise stated. As used herein, the terms “include”or “have” are used to indicate that there are features, numerals, steps,operations, components, parts or combinations thereof as describedherein, but do not exclude the presence or possibility of addition ofone or more features, numerals, steps, operations, components, parts orcomponents thereof.

Unless defined otherwise, all the terms used herein including technicalor scientific terminology have the same meaning as are generallyunderstood by those skilled in the art. Such terms as defined in thedictionary as commonly used should be construed to have the samemeanings as those understood in the context of the related technology,and unless otherwise defined, should not be understood ideally or tooformally.

Hereinafter, preferred embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.For ease of description, the same reference numerals are used to denotethe same components throughout the specification and the drawings, andthe description thereof is not repeated.

According to an example embodiment of the present invention, encodingand decoding including inter/intra prediction, transform, quantization,and entropy encoding may be performed using an extended macroblock sizeof 32×32 pixels or more to be applicable to high-resolution imageshaving a resolution of HD (High Definition) or higher, and encoding anddecoding may be conducted using a recursive coding unit (CU) structurethat will be described below.

FIG. 1 is a conceptual view illustrating a recursive coding unitstructure according to an example embodiment of the present invention.

Referring to FIG. 1, each coding unit CU has a square shape and may havea variable size of 2N×2N (unit: pixels). Inter prediction, intraprediction, transform, quantization, and entropy encoding may beperformed on a per-coding unit basis. The coding unit CU may include amaximum coding unit LCU and a minimum coding unit SCU. The size of themaximum or minimum coding unit LCU or SCU may be represented by powersof 2 which are 8 or more.

According to an example embodiment, the coding unit CU may have arecursive tree structure. FIG. 1 illustrates an example where a side ofthe maximum coding unit LCU (or CU0) has a size of 2N0 which is 128(N0=64) while the maximum level or level depth is 5. The recursivestructure may be represented by a series of flags. For example, in thecase that a coding unit CUk whose level or level depth is k has a flagvalue of 0, coding on the coding unit CUk is performed on the currentlevel or level depth. When the flag value is 1, the coding unit CUk issplit into four independent coding units CUk+1 having a level or leveldepth of k+1 and a size of Nk+1×Nk+1. In this case, the coding unitCUk+1 may be recursively processed until its level or level depthreaches the permissible maximum level or level depth. When the level orlevel depth of the coding unit CUk+1 is the same as the permissiblemaximum level or level depth (which is, e.g., 4 as shown in FIG. 4), anyfurther splitting is not permissible.

The size of the maximum coding unit LCU and the size of the minimumcoding unit SCU may be included in a sequence parameter set (SPS). Thesequence parameter set SPS may include the permissible maximum level orlevel depth of the maximum coding unit LCU. For example, in the exampleillustrated in FIG. 2, the permissible maximum level or level depth is5, and when the side of the maximum coding unit LCU has a size of 128pixels, five coding unit sizes, such as 128×128 (LCU), 64×64, 32×32,16×16, and 8×8 (SCU), may be possible. That is, given the size of themaximum coding unit LCU and the permissible maximum level or leveldepth, the permissible size of the coding unit may be determined.

Use of the above-described recursive coding unit structure may providethe following advantages.

First, a size larger than that of the existing 16×16 macro-block may besupported. If an image region of interest is homogeneous, the maximumcoding unit LCU may express the image region of interest with a smallernumber of symbols than when using a number of small blocks.

Second, compared to when using a fixed size of macro-block, any size ofmaximum coding unit LCU may be supported, so that the codec may beeasily optimized to various contents, applications, and apparatuses.That is, the size of the maximum coding unit LCU, the maximum level orlevel depth may be properly selected so that the hierarchical blockstructure may be optimized further than the target application.

Third, irrespective of whether it is a macro-block, sub-macro-block, orextended macro-block, a single unit type of a coding unit LCU is used sothat the multilevel hierarchical structure may be simply represented byusing the size of the maximum coding unit LCU, the maximum level (or themaximum level depth), and a series of flags. When used together withsize-independent syntax representation, the coding unit LCU is enough toindicate one generalized size of syntax item for the remaining codingtools, and such conformity may simplify actual parsing processes. Themaximum level value (or maximum level depth value) may be any value andmay have a value larger than a value permitted in the existing H.264/AVCencoding scheme. All syntax elements may be indicated in a consistentmanner independent from the size of the coding unit CU by using thesize-independent syntax representation. The splitting process for thecoding unit may be recursively indicated, and syntax elements for theleaf coding unit (the last coding unit in the level) may be defined tothe same size regardless of the size of the coding unit. The aboverepresentation is very effective in reducing parsing complexity and maymake the representation further clarified when a high level or leveldepth is allowed.

If the hierarchical splitting process is complete, inter prediction orintra prediction may be performed on the leaf node of the coding unithierarchical unit without being further split. This leaf coding unit isused as the prediction unit PU which is a basic unit of the interprediction or intra prediction.

For inter prediction or intra prediction, partitioning is fulfilled onthe leaf coding unit. That is, partitioning is performed on theprediction unit PU. Here, the prediction unit PU is a basic unit forinter prediction or intra prediction and may be an existing macro-blockunit or sub-macro-block unit, or an extended macro-block unit having asize of 32×32 pixels or more or a coding unit.

All information related to prediction (motion vector, difference betweenmotion vectors, etc) is transmitted to decoder in a unit of predictionunit which is a basic unit of inter-prediction.

For inter prediction or intra prediction partitioning may includeasymmetrical partitioning, geometrical partitioning in any shape otherthan square, or partitioning along an edge direction, which are nowdescribed in greater detail.

FIGS. 2 to 5 are conceptual views illustrating asymmetric partitioningaccording to an embodiment.

When the prediction unit PU for inter prediction or intra prediction hasa size of M×M (M is a natural number. The unit of the size is pixel),asymmetric partitioning is performed along a horizontal or verticaldirection of the coding unit. FIGS. 3 to 5 illustrate examples where thesize of the prediction unit PU is 64×64, 32×32, 16×16, 8×8 pixels. FIGS.3 and 4 illustrate asymmetric partition where the size of the predictionunit PU is more than 16×16 pixels which is the size of macroblock.

Referring to FIG. 2, in the case of having a size of 64×64, asymmetricpartitioning is conducted along a horizontal direction to split theprediction unit into a partition P11 a having a size of 64×16 and apartition P21 a having a size of 64×48 or into a partition P12 a havinga size of 64×48 and a partition P22 a having a size of 64×16. Or,asymmetric partitioning is performed along a vertical direction to splitthe prediction unit into a partition P13 a having a size of 16×64 and apartition P23 a having 48×64 or into a partition P14 a having a size of48×64 and a partition P24 a having a size of 16×64.

Referring to FIG. 3, in the case of having a size of 32×32, theprediction unit may be subjected to horizontal-direction asymmetricpartitioning to be split into a partition P11 b having a size of 32×8and a partition P21 b having a size of 32×24 or into a partition P12 bhaving a size of 32×24 and a partition P22 b having a size of 32×8. Or,the prediction unit may be subjected to vertical-direction asymmetricpartitioning to be split into a partition P13 b having a size of 8×32and a partition P23 b having a size of 24×32 or into a partition P14 bhaving a size of 24×32 and a partition P24 b having a size of 8×32.

Referring to FIG. 4, in the case of having a size of 16×16, theprediction unit PU may be subjected to horizontal-direction asymmetricpartitioning to be split into a partition P11 c having a size of 16×4and a partition P21 c having a size of 16×12 or (although not shown inthe drawings) into an upper partition having a size 16×12 and a lowerpartition having a size of 16×4. Further, although not shown in thedrawings, the prediction unit PU may be subjected to vertical-directionasymmetric partitioning to be split into a left partition having a sizeof 4×16 and a right partition having a size of 12×16 or into a leftpartition having a size of 12×16 and a right partition having a size of4×16.

Referring to FIG. 5, in the case of having a size of 8×8, the predictionunit PU may be subjected to horizontal-direction asymmetric partitioningto be split into a partition P11 d having a size of 8×2 and a partitionP21 d having a size of 8×6 or (although not shown in the drawings) intoan upper partition having a size 8×6 and a lower partition having a sizeof 8×2. Further, although not shown in the drawings, the prediction unitPU may be subjected to vertical-direction asymmetric partitioning to besplit into a left partition having a size of 2×8 and a right partitionhaving a size of 6×8 or into a left partition having a size of 6×8 and aright partition having a size of 2×8.

FIG. 6 is a conceptual view illustrating an intra-prediction encodingmethod using an asymmetric pixel block according to an exampleembodiment of the present invention.

FIGS. 7 to 9 are conceptual views illustrating an intra-predictionencoding method using an asymmetric pixel block according to anotherexample embodiment of the present invention. FIGS. 6 to 9 illustrate anexample of intra prediction when the asymmetric partitioning describedin connection with FIGS. 2 to 5 is used. However, the present inventionis not limited thereto. The intra-prediction encoding method illustratedin FIGS. 6 to 9 may also apply to when various types of asymmetricpartitioning illustrated in FIGS. 2 to 5 are used.

FIG. 6 is a view for describing a prediction mode to perform intraprediction on partition P11 d having a size of 8×2 obtained byperforming asymmetric partitioning on the prediction unit PU whose sizeis 8×8 in a horizontal direction.

Referring to FIG. 6, a pixel value in partition P11 d having a size of8×2 is predicted using a pixel value in a block previously encoded alongthe prediction directions including a vertical direction (predictionmode 0), horizontal direction (prediction mode 1), average valueprediction (prediction mode 2), diagonal down-right direction(prediction mode 3), and diagonal down-left direction (prediction mode4).

For example, in the case of prediction mode 0, as the prediction pixelvalue in the partition P11 d having a size of 8×2, the pixel valuepositioned along the vertical direction in the previously encoded upperblock is used.

In the case of prediction mode 1, as the prediction pixel value in thepartition P11 d having a size of 8×2, the pixel value positioned alongthe horizontal direction in the previously encoded left block is used.

In the case of prediction mode 2, as the prediction pixel value in thepartition P11 d having a size of 8×2, the average value of the pixels inthe previously encoded left and upper blocks is used.

In the case of prediction mode 3, as the prediction pixel value in thepartition P11 d having a size of 8×2, the pixel value positioned alongthe diagonal down-right direction in the previously encoded upper blockis used. In the case of prediction mode 3, when the pixel in the upperblock of the partition P11 d is not sufficient, two pixels in the upperand right block may be used to make it up.

In the case of prediction mode 4, as the prediction pixel value in thepartition P11 d having a size of 8×2, the pixel value positioned alongthe diagonal down-left direction in the previously encoded left andupper block is used.

FIG. 7 illustrates a prediction mode for performing intra prediction onpartition P21 d having a size of 8×6 obtained by performing asymmetricpartitioning on the prediction unit PU whose size is 8×8 in thehorizontal direction.

Referring to FIG. 7, a pixel value in partition P21 d having a size of8×6 is predicted using a pixel value in a block previously encoded alongthe prediction directions including a vertical direction (predictionmode 0), horizontal direction (prediction mode 1), average valueprediction (prediction mode 2), diagonal down-right direction(prediction mode 3), and diagonal down-left direction (prediction mode4).

For example, in the case of prediction mode 0, as the prediction pixelvalue in the partition P21 d having a size of 8×6, the pixel valuepositioned along the vertical direction in the previously encoded upperblock is used.

In the case of prediction mode 1, as the prediction pixel value in thepartition P21 d having a size of 8×6, the pixel value positioned alongthe horizontal direction in the previously encoded left block is used.

In the case of prediction mode 2, as the prediction pixel value in thepartition P21 d having a size of 8×6, the average value of the pixels inthe previously encoded left and upper blocks is used.

In the case of prediction mode 3, as the prediction pixel value in thepartition P21 d having a size of 8×6, the pixel value positioned alongthe diagonal down-right direction in the previously encoded upper blockis used. In the case of prediction mode 3, when the pixel in the upperblock of the partition P21 d is not sufficient, six pixels in the upperand right block may be used to make it up.

In the case of prediction mode 4, as the prediction pixel value in thepartition P21 d having a size of 8×6, the pixel value positioned alongthe diagonal down-left direction in the previously encoded left andupper block is used.

FIG. 8 illustrates a prediction mode for performing intra prediction onpartition P11 c having a size of 16×4 obtained by performing asymmetricpartitioning on the prediction unit PU whose size is 16×16 in thehorizontal direction.

Referring to FIG. 8, a pixel value in partition P11 c having a size of16×4 is predicted using a pixel value in a block previously encodedalong the prediction directions including a vertical direction(prediction mode 0), horizontal direction (prediction mode 1), averagevalue prediction (prediction mode 2), diagonal down-right direction(prediction mode 3), and diagonal down-left direction (prediction mode4).

For example, in the case of prediction mode 0, as the prediction pixelvalue in the partition P11 e having a size of 16×4, the pixel valuepositioned along the vertical direction in the previously encoded upperblock is used.

In the case of prediction mode 1, as the prediction pixel value in thepartition P11 e having a size of 16×4, the pixel value positioned alongthe horizontal direction in the previously encoded left block is used.

In the case of prediction mode 2, as the prediction pixel value in thepartition P11 c having a size of 16×4, the average value of the pixelsin the previously encoded left and upper blocks is used.

In the case of prediction mode 3, as the prediction pixel value in thepartition P11 c having a size of 16×4, the pixel value positioned alongthe diagonal down-right direction in the previously encoded upper blockis used. In the case of prediction mode 3, when the pixel in the upperblock of the partition P11 e is not sufficient, four pixels in the upperand right block may be used to make it up.

In the case of prediction mode 4, as the prediction pixel value in thepartition P11 c having a size of 16×4, the pixel value positioned alongthe diagonal down-left direction in the previously encoded left andupper block is used.

FIG. 9 illustrates a prediction mode for performing intra prediction onpartition P11 b having a size of 32×8 obtained by performing asymmetricpartitioning on the prediction unit PU whose size is 32×32 in thehorizontal direction.

Referring to FIG. 9, a pixel value in partition P11 b having a size of32×8 is predicted using a pixel value in a block previously encodedalong the prediction directions including a vertical direction(prediction mode 0), horizontal direction (prediction mode 1), averagevalue prediction (prediction mode 2), diagonal down-right direction(prediction mode 3), and diagonal down-left direction (prediction mode4).

For example, in the case of prediction mode 0, as the prediction pixelvalue in the partition P11 b having a size of 32×8, the pixel valuepositioned along the vertical direction in the previously encoded upperblock is used.

In the case of prediction mode 1, as the prediction pixel value in thepartition P11 b having a size of 32×8, the pixel value positioned alongthe horizontal direction in the previously encoded left block is used.

In the case of prediction mode 2, as the prediction pixel value in thepartition P11 b having a size of 32×8, the average value of the pixelsin the previously encoded left and upper blocks is used.

In the case of prediction mode 3, as the prediction pixel value in thepartition P11 b having a size of 32×8, the pixel value positioned alongthe diagonal down-right direction in the previously encoded upper blockis used. In the case of prediction mode 3, when the pixel in the upperblock of the partition P11 b is not sufficient, eight pixels in theupper and right block may be used to make it up.

In the case of prediction mode 4, as the prediction pixel value in thepartition P11 b having a size of 32×8, the pixel value positioned alongthe diagonal down-left direction in the previously encoded left andupper block is used.

FIGS. 6 to 9 illustrate examples of using a predetermined number ofprediction modes for each size of the prediction unit for the asymmetricpartition block, and prediction modes along the other directions (notshown) for each prediction unit may also be used. For example, the intraprediction may be performed along lines formed at the same predeterminedangle (e.g., 22.5° or 11.25°) all over the entire direction within 360°using pixel values in the previously encoded left and upper blocks. Or,any angle may be previously designated by the encoder so that the intraprediction may be performed along a line defined according to thedesignated angle. To designate the angle, for example, a slope with dxalong the horizontal direction and dy along the vertical direction maybe defined, and information on dx and dy may be transferred from theencoder to the decoder. Predetermined angle information may also betransferred from the encoder to the decoder.

FIG. 10 is a concept view illustrating an intra-prediction encodingmethod based on planar prediction according to another exampleembodiment of the present invention.

In the case that an extended macro-block having a size of 16×16 or moreis used to encode a high-resolution image having a HD or higherresolution or the size of the prediction unit is increased to 8×8 ormore, if the existing intra prediction mode applies to the rightmost andlowermost pixel value of the prediction unit, distortion is created bythe prediction, thus rendering it difficult to smooth the image as asmooth one.

In such case, a separate planar mode may be defined, and when the planarmode flag is activated, as shown in FIG. 10, in order to obtainpredicted pixel value of the rightmost and lowermost pixel (1010) of theprediction unit, a linear interpolation may be performed using value ofthe pixels (1001 and 1003) and/or the value of inner pixels ofprediction block. The pixel 1001 is located in previously encoded upperblock of the prediction unit and corresponds to the rightmost andlowermost pixel (1010) in a vertical direction. The pixel 1003 islocated in previously encoded left block of the prediction unit andcorresponds to the rightmost and lowermost pixel (1010) in a horizontaldirection. The inner pixels are pixels which are located inside theprediction block and the inner pixels correspond to the rightmost andlowermost pixel (1010) in a horizontal direction and a verticaldirection.

Namely, when the planar mode flag is activated, as shown in FIG. 10, inorder to obtain predicted pixel value of the rightmost and lowermostpixel (for example pixel 1010) of the prediction unit, a linearinterpolation may be performed using value of the pixels (1001 and1003). The pixel 1001 is located in previously encoded upper block ofthe prediction unit and corresponds to the rightmost and lowermost pixel(1010) in a vertical direction. The pixel 1003 is located in previouslyencoded left block of the prediction unit and corresponds to therightmost and lowermost pixel (1010) in a horizontal direction.

Alternatively, when the planar mode flag is activated, as shown in FIG.10, in order to obtain predicted pixel value of the rightmost andlowermost pixel (for example pixel 1010) of the prediction unit, alinear interpolation may be performed using value of the pixels (1001and 1003) and inner pixels. The pixel 1001 is located in previouslyencoded upper block of the prediction unit and corresponds to therightmost and lowermost pixel (1010) in a vertical direction and thepixel 1003 is located in previously encoded left block of the predictionunit and corresponds to the rightmost and lowermost pixel (1010) in ahorizontal direction. The inner pixels are located inside the predictionblock and the inner pixels correspond to the rightmost and lowermostpixel (1010) in a horizontal direction and a vertical direction. Whenthe planar mode flag is activated, the rightmost and lowermost pixel(1010) value of the prediction unit may be transferred from the encoderto the decoder. Here, vertically and/or horizontally directionalcorresponding pixel values (1001, 1003) in the previously encoded leftside block and upper end block indicates pixel values of the pixels inthe left side block and upper end block among already encoded blocksadjacent to the prediction block in case the current prediction unitconsists of 8×8 prediction blocks as shown in FIG. 10, a horizontallydirectional corresponding pixel value of the pixel 1010 positioned atthe rightmost and lowermost end of the prediction unit indicates valueof the pixel 1003, and a vertically directional corresponding pixelvalue of the pixel 1010 positioned at the rightmost and lowermost end ofthe prediction unit indicates value of the pixel 1001, and ahorizontally directional internal prediction pixel value in theprediction block indicates value(s) of at least one of pixels positionedalong the horizontal direction between the pixel 1003 and the rightmostand lowermost pixel 1010, and a vertically directional correspondinginternal prediction pixel value in the prediction block indicatesvalue(s) of at least one of pixels arranged along the vertical directionbetween the pixel 1001 and the rightmost and lowermost pixel 1010.

Further, in case the planar prediction mode flag is activated, theprediction pixel value of an internal pixel of the prediction unit maybe obtained by performing bilinear interpolation using vertically and/orhorizontally directional corresponding pixel values of the pixels in theleft side block and upper end block that are previously encoded and/orvertically and/or horizontally directional corresponding internalboundary prediction pixel values in the prediction unit (for example,the vertically and/or horizontally directional corresponding internalboundary prediction pixel values indicates value(s) of at least one ofpixels positioned along the horizontal direction between the pixel 1003and the rightmost and lowermost pixel 1010 or value(s) of at least oneof pixels arranged along the vertical direction between the pixel 1001and the rightmost and lowermost pixel 1010). Here, the prediction pixelvalues of the internal pixels of the prediction unit indicatesprediction pixel values of internal pixels arranged along the horizontaldirection in the prediction block (since 8×8 blocks are shown in FIG.10, there are 8 horizontal lines, and the prediction pixel values ofinternal pixels arranged along the horizontal direction in theprediction block indicates prediction pixel values of the 8 internalpixels arranged along the direction of each of the 8 horizontal lines)or prediction pixel values of internal pixels arranged along thevertical direction in the prediction block (since 8×8 blocks are shownin FIG. 10, there are 8 vertical lines, and the prediction pixel valuesof internal pixels arranged along the vertical direction in theprediction block indicates prediction pixel values of the 8 internalpixels arranged along the vertical direction of each of the 8 verticallines).

In case, in FIG. 10, the prediction pixel value of the internal pixel ofthe prediction unit is obtained, the vertically and/or horizontallydirectional corresponding pixel values in the previously encoded leftside block and upper end block indicate pixel values of the pixels inthe left side block and the upper end block of the previously encodedblocks adjacent to the prediction block. In case the current predictionunit consists of 8×8 prediction blocks as shown in FIG. 10, thehorizontally directional corresponding pixel values of the 8 pixels ofthe rightmost line of the prediction unit (i.e. 8 pixels from the top tothe bottom) indicate pixel values of the pixels arranged at the sameposition along the horizontal direction as the corresponding pixel ofthe rightmost line of the prediction unit among the previously encodedleft side block adjacent to the prediction block, and the verticallydirectional corresponding pixel values of the 8 pixels of the lowermostend line of the prediction unit (i.e. 8 pixels from the leftmost side tothe rightmost side) indicate pixel values of the pixels arranged at thesame position along the vertical direction as the corresponding pixel ofthe lowermost line of the prediction unit.

Further, in case, in FIG. 10, the prediction pixel values of theinternal pixels of the prediction unit are obtained, the verticallyand/or horizontally directional corresponding internal boundaryprediction pixel values of the pixels in the prediction unit indicatepixel values (predicted pixel values) of the pixels positioned at thelowermost line or at the rightmost line in the prediction block. In casethe current prediction unit consists of 8×8 prediction blocks as shownin FIG. 10, for example, the internal boundary prediction pixel value ofthe pixel corresponding to the right-sided seventh pixel among 8 pixelson the fifth horizontal line from the top of the prediction unit may bethe pixel value (or predicted pixel value) of the rightmost pixel amongthe 8 pixels on the fifth horizontal line from the top of the predictionunit. In such case, the predicted pixel value of the right-sided seventhpixel among the 8 pixels on the fifth horizontal line from the top ofthe prediction unit may be obtained by performing bilinear interpolationusing the pixel value (or predicted pixel value) of the rightmost pixelamong the 8 pixels on the fifth horizontal line from the top of theprediction unit and the pixel value of the previously encoded pixelarranged at the same position along the horizontal direction as theright-sided seventh pixel among the 8 pixels on the fifth horizontalline from the top of the prediction unit among the pixel values of thepixels in the previously encoded left side block adjacent to theprediction block.

Further, in case, in FIG. 10, the predicted pixel values of the internalpixels of the prediction unit are obtained, vertically and/orhorizontally directional corresponding internal boundary predictionpixel values of the pixels in the prediction unit, when the currentprediction unit consists of 8×8 prediction blocks as shown in FIG. 10,for example, the internal boundary prediction pixel value of the pixelcorresponding to the seventh pixel along the vertical direction from thetop among the 8 pixels on the right-sided fifth vertical line from theleftmost side of the prediction unit may be a pixel value of the pixellocated at the lowermost end of the 8 pixels on the right-sided fifthvertical line from the leftmost side of the prediction unit.

In such case, the prediction pixel value of the seventh pixel along thevertical direction from the top among the 8 pixels on the right-sidedfifth vertical line from the leftmost side of the prediction unit may beobtained by performing bilinear interpolation using the pixel value (orprediction pixel value) of the pixel located at the lowermost end amongthe 8 pixels on the right-sided fifth vertical line from the leftmostside of the prediction unit and pixel value (or prediction pixel value)of the previously encoded pixel arranged at the same position along thevertical direction as the seventh pixel along the vertical directionfrom the top among the 8 pixels on the right-sided fifth vertical linefrom the leftmost side of the prediction unit among the pixel values ofthe pixels in the previously encoded upper side block adjacent to theprediction block.

Meanwhile, in case the planar prediction mode flag is activated, thepixel value of the rightmost and lowermost end pixel of the predictionunit may be transmitted from the encoder to the decoder. Further, thepixel values of pixels located at the rightmost line of FIG. 10 may beobtained by performing linear interpolation using the rightmost anduppermost pixel 1001 and the rightmost and lowermost pixel 1010 thathave been transmitted from the encoder. The pixel values of the pixelslocated at the lowermost line of FIG. 10 may be obtained by performinglinear interpolation using the leftmost and lowermost pixel 1003 and therightmost and lowermost pixel 1010 that have been transmitted from theencoder.

FIG. 11 is a conceptual view illustrating an intra-prediction encodingmethod based on planar prediction according to another exampleembodiment of the present invention.

When the planar prediction mode flag is activated, as shown in FIG. 11,a reference prediction unit for a current prediction unit having a firstsize—for example, 8×8 pixels in FIG. 11—which is included in the Nthpicture which is a current picture to be encoded is determined at theN−1th picture positioned temporarily before the Nth picture. To obtainthe prediction pixel value of the rightmost and lowermost pixel in thecurrent prediction unit, not only vertical- and horizontal-directionallycorresponding pixel values in the previously encoded left and upperblocks 213, which are adjacent to the current prediction unit, but alsovertical- and horizontal-directionally corresponding pixel values in thepreviously encoded left and upper blocks 233, which are adjacent to thecorresponding prediction unit of the N−1th picture are used to calculatetheir average values or to perform linear interpolation.

Or, to obtain the prediction pixel value of the rightmost and lowermostpixel in the current prediction unit, vertical- andhorizontal-directionally corresponding inner pixel values in the currentprediction unit of the Nth picture, as well as vertical- andhorizontal-directionally corresponding pixel values in the previouslyencoded left and upper blocks 213, which are adjacent to the currentprediction unit, and vertical- and horizontal-directionallycorresponding pixel values in the previously encoded left and upperblocks 233, which are adjacent to the corresponding prediction unit ofthe N−1th picture are used to calculate their average values or toperform linear interpolation.

Further, to obtain the prediction pixel value of the rightmost andlowermost pixel in the current prediction unit, vertical- andhorizontal-directionally corresponding inner pixel values of therightmost and lowermost pixel in the corresponding unit of the N−1thpicture, as well as vertical- and horizontal-directionally correspondinginner pixel values in the current prediction unit of the Nth picture,vertical- and horizontal-directionally corresponding pixel values in thepreviously encoded left and upper blocks 213, which are adjacent to thecurrent prediction unit, and vertical- and horizontal-directionallycorresponding pixel values in the previously encoded left and upperblocks 233, which are adjacent to the corresponding prediction unit ofthe N−1th picture are used to calculate their average values or toperform linear interpolation.

Also, in the case that the planar prediction mode flag is activated, theprediction pixel value of the inner pixel in the prediction unit of theNth picture may be obtained by performing bilinear interpolation usingvertical- and horizontal-directionally corresponding inner boundarypixel values in the corresponding prediction unit of the N−1th picture,vertical- and horizontal-directionally corresponding pixel values in thepreviously encoded left and upper blocks in the corresponding predictionunit of the N−1th picture, vertical- and horizontal-directionallycorresponding inner boundary pixel values in the current prediction unitof the Nth picture and/or vertical- and horizontal-directionallycorresponding pixel values in the previously encoded left and upperblocks in the current prediction unit of the Nth picture.

Although FIG. 11 illustrates an example where intra prediction isconducted using the current prediction unit of the Nth picture and acorresponding prediction unit of the N−1th picture, the presentinvention is not limited thereto. For example, the intra prediction mayalso be performed using the current prediction unit of the Nth pictureand a corresponding prediction unit of the N+1th picture, using thecurrent prediction unit of the Nth picture and corresponding predictionunits of the N−1th picture and the N+1th picture, or using the currentprediction unit of the Nth picture and corresponding prediction units ofthe N−2th picture, N−1th picture, N+1th picture, and N+2th picture.

The current prediction unit having the second size may have a squareshape with 8×8, 16×16, or 32×32 pixels or may have an asymmetric shapeas illustrated in FIGS. 2 to 5. In the case that the current predictionunit has an asymmetric shape as illustrated in FIGS. 2 to 6, theembodiments described in connection with FIGS. 10 and 11 may apply inorder to perform inter prediction.

That is, the intra prediction encoding method based on the planarprediction as shown in FIGS. 10 and 11 may be applicable to intraprediction encoding/decoding for pixel blocks the prediction unit ofwhich has a symmetrical shape, such as a rectangle or square, as well aspixel blocks the prediction unit of which has an asymmetrical shape orany geometrical shape.

FIG. 12 is conceptual view illustrating geometrical partitioningaccording to another example embodiment of the present invention.

FIG. 12 illustrates an example where the prediction unit PU is subjectedto geometrical partitioning so that the split partitions have a shapeother than square.

Referring to FIG. 12, for the prediction unit, a geometrical boundaryline L between partitions may be defined as follows. The prediction unitPU is divided into four quadrants by x and y axes passing through thecenter O of the prediction unit PU. A vertical line is drawn from thecenter O to the boundary line L. Then, any possible boundary line Lpositioned in any direction may be specified by a distance p from thecenter O to the boundary line L and an angle θ from the x axis to thevertical line in a counterclockwise direction.

For inter or intra prediction, the prediction unit PU is divided intofour quadrants with respect to its center. The second quadrant which isthe upper and left portion of the prediction unit PU is split into apartition, and the remaining L-shaped quadrants are split into apartition. As used herein, the “portion” of the prediction unit PU,which corresponds to a split partition or several split partitions, isalso called “block”. Or, the third quadrant which is the lower and leftportion of the prediction unit PU is split into a partition′, and theremaining quadrants are split into a partition. Alternatively, the firstquadrant which is the upper and right portion of the prediction unit PUis split into a partition, and the remaining quadrants are split into apartition. Also, the lower and right portion of the prediction unit PUwhich corresponds to the fourth quadrant is split into a partition, withthe remaining quadrants slit into a partition. Further, the fourthquadrant, the lower and right portion of the prediction unit PU, issplit into a partition, with the remaining quadrants split into apartition.

As described above, the prediction unit may be split so that a splitpartition has an L shape. Accordingly, in the case that, uponpartitioning, there is a moving object in an edge block, e.g., the upperand left, upper and right, lower and right, or lower and left block, itmay provide more effective encoding than when the prediction unit PU issplit into four blocks. Depending on the edge block in which the movingobject is positioned among the four partitions, the correspondingpartition may be selected and used.

The size of the block used for motion estimation may vary. In addition,according to one example embodiment, when asymmetric partitioning orgeometrical partitioning applies, the shape of the block may have notonly the existing square shape but also geometrical shapes, such as arectangular or other asymmetric shapes, an ‘L’ shape, or a triangularshape, as shown in FIGS. 2 to 9.

Also in the case of the above-described geometrical block partitioningincluding the block partitioning described in connection with FIG. 10,the prediction modes applied in FIGS. 6 to 9 may be transformed andutilized to perform intra prediction on the geometrical blocks.

FIG. 13 is a block diagram illustrating a configuration of an imageencoding apparatus to perform intra-prediction encoding according to anexample embodiment of the present invention.

Referring to FIG. 13, the image encoding apparatus includes an encoder630. The encoder 630 includes an inter predicting unit 632, an intrapredicting unit 635, a subtractor 637, a transform unit 639, aquantization unit 641, an entropy encoding unit 643, an inversequantization unit 645, an inverse transform unit 647, an adder 649, anda frame buffer 651. The inter predicting unit 632 includes a motionpredicting unit 631 and a motion compensating unit 633.

The encoder 630 performs encoding on an input image. The input image maybe used on a per-prediction unit PU basis for inter prediction in theinter predicting unit 632 or for intra prediction in the intrapredicting unit 635.

The size of the prediction unit applying to inter prediction or intraprediction may be determined according to temporal frequencycharacteristics of a frame (or picture) stored in a buffer (not shown)included in the encoder after the input image is stored in the buffer.For example, the prediction unit determining unit 610 analyzes thetemporal frequency characteristics of the n−1th frame (or picture) andthe nth frame (or picture), and if the analyzed temporal frequencycharacteristics value is less than a preset first threshold value,determines the size of the prediction unit as 64×64 pixels. If theanalyzed temporal frequency characteristics value is equal to and morethan the preset first threshold value and less than a second thresholdvalue, the size of the prediction unit is determined as 32×32 pixels,and if the analyzed temporal frequency characteristics value is equal toor more than the preset second threshold value, the size of theprediction unit is determined as 16×16 pixels or less. Here, the firstthreshold value refers to a temporal frequency characteristics valuewhen a variance between frames (or pictures) is smaller than the secondthreshold value.

The size of the prediction unit applying to inter prediction or intraprediction may be determined according to spatial frequencycharacteristics of a frame (or picture) stored in a buffer (not shown)included in the encoder after the input image is stored in the buffer.For example, in the case that the input frame (or picture) has highuniformity or homogeneity, the size of the prediction unit may be set tobe large, for example, to 32×32 pixels or more, and in the case that theinput frame (or picture) has low uniformity or homogeneity (that is,when spatial frequency is high), the size of the prediction unit may beset to be small, for example, to 16×16 pixels or less.

Although not shown in FIG. 13, the operation of determining the size ofthe prediction unit may be performed by an encoding controller (notshown) receiving the input image or by a separate prediction unitdetermining unit (not shown) receiving the input image. For example, thesize of the prediction unit may be 16×16, 32×32, or 64×64 pixels.

As described above, the prediction unit information including the sizeof the prediction unit determined for inter or intra prediction isprovided to the entropy encoding unit 643 and provided to the encoder630 on the basis of the prediction unit having the determined size.Specifically, in the case that encoding and decoding are performed usingthe extended macro-block and the size of the extended macro-block, theprediction block information may include information on the size of themacro-block or the extended macro-block. Here, the size of the extendedmacro-block refers to 32×32 pixels or more, including, for example,32×32, 64×64, or 128×128 pixels. In the case that the above-mentionedrecursive coding unit CU is used to perform encoding and decoding, theprediction unit information may include, instead of the information onthe size of the macro-block, information on the size of the maximumcoding unit LCU to be used for inter or intra prediction, that is, thesize of the prediction unit, and further, the prediction unitinformation may include the size of the maximum coding unit LCU, thesize of the minimum coding unit SCU, the maximum permissible level orlevel depth, and flag information.

The encoder 630 performs encoding on the prediction unit having thedetermined size.

The inter predicting unit 632 splits the prediction unit to be currentlyencoded by the above-described asymmetric partitioning or geometricalpartitioning and performs motion estimation on a per-split partitionbasis to generate a motion vector.

The motion predicting unit 631 splits the provided current predictionunit by various partitioning methods and searches a region similar tothe partitioned block to be currently encoded in at least one referencepicture (which is encoded and stored in the frame buffer 651) positionedbefore and/or behind the currently encoded picture for each partitionedblock, thereby generating a motion vector on a per-block basis. The sizeof the block used for motion estimation may vary, and according to anembodiment, when asymmetric partitioning or geometrical partitioningapplies, the shape of the block may have not only the existing squareshape but also geometrical shapes, such as a rectangular or otherasymmetric shapes, an ‘L’ shape, or a triangular shape, as shown inFIGS. 2 to 9.

The motion compensating unit 633 generates a prediction block (orpredicted prediction unit) by performing motion compensation using thereference picture and the motion vector generated from the motionpredicting unit 631.

The inter predicting unit 632 performs block merging on the block andobtains a motion parameter for each merged block. The obtained motionparameter is transferred to the decoder.

The intra predicting unit 635 may perform intra-prediction encodingusing a pixel correlation between blocks. The intra predicting unit 635performs intra prediction that seeks the prediction block of the currentprediction unit by predicting a pixel value from previously encodedpixel values in the block of the current frame (or picture) according tovarious embodiments as described in connection with FIGS. 6 to 11.

The subtractor 637 performs subtraction between the prediction block (orpredicted prediction unit) provided from the motion compensating unit633 and the current block (or current prediction unit) to generate aresidue, and the transform unit 639 and the quantization unit 641respectively perform DCT (Discrete Cosine Transform) and quantization onthe residue. Here, the transform unit 639 may perform transform based onthe prediction unit size information provided from the prediction unitdetermining unit 1810. For example, the transform unit 639 may conducttransform to a size of 32×32 or 64×64 pixels. Or, the transform unit 639may perform transform on the basis of a separate transform unit TUindependently from the prediction unit size information provided fromthe prediction unit determining unit 610. For example, the transformunit TU size may have the minimum of 4×4 pixels to the maximum of 64×64pixels. Or, the maximum size of the transform unit TU may be more than64×64 pixels—for example, 128×128 pixels. The transform unit sizeinformation may be included in the transform unit information andtransferred to the decoder.

The entropy encoding unit 643 performs entropy encoding on headerinformation including quantized DCT coefficients, motion vector,determined prediction unit information, partition information, andtransform unit information, thereby generating a bit stream.

The inverse quantization unit 645 and the inverse transform unit 647respectively perform inverse quantization and inverse transform on thedata quantized by the quantization unit 641. The adder 649 adds theinverse transformed data to the predicted prediction unit provided fromthe motion compensating unit 633 to reconstruct the image and providesthe reconstructed image to the frame buffer 651, so that the framebuffer 651 stores the stored image.

FIG. 14 is a flowchart illustrating an image encoding method appliedwith intra-prediction encoding according to an example embodiment of thepresent invention.

Referring to FIG. 14, when an image is input to the encoding apparatus(step S1401), for the input image, the prediction unit for inter orintra prediction is split by the above-described asymmetric orgeometrical partitioning method (step S1403).

In the case that the intra prediction mode is activated, the partitionedasymmetric block or geometric block is applied with the intra predictionmethod described in connection with FIGS. 6 to 11, thereby performingintra prediction (step S1405). Or, when the inter prediction mode isactivated, the prediction block (or predicted prediction unit) isgenerated by searching a region similar to the partitioned block to becurrently encoded in at least one reference picture (which is encodedand stored in the frame buffer 651) positioned before and/or behind thecurrently encoded picture for each partitioned block, thereby generatinga motion vector on a per-block basis, followed by performing motioncompensation using the generated motion vector and picture.

Next, the encoding apparatus obtains a difference between the currentprediction unit and the predicted (intra-predicted or inter-predicted)prediction unit to generate a residue, then performing transform andquantization on the generated residue (step S1407). Thereafter, theencoding apparatus entropy-encodes the header information includingquantized DCT coefficients and motion parameter and generates a bitstream (step S1409).

FIG. 15 is a block diagram illustrating a configuration of an imagedecoding apparatus according to an example embodiment of the presentinvention.

Referring to FIG. 15, the decoding apparatus includes an entropydecoding unit 731, an inverse quantization unit 733, an inversetransform unit 735, a motion compensating unit 737, an intra predictingunit 739, a frame buffer 741, and an adder 743.

The entropy decoding unit 731 receives a compressed bit stream andperforms entropy decoding on the compressed bit stream therebygenerating a quantized coefficient. The inverse quantization unit 733and the inverse transform unit 735 respectively perform inversequantization and inverse transform on the quantized coefficient toreconstruct the residue.

The header information decoded by the entropy decoding unit 731 mayinclude the prediction unit size information which may include, e.g.,16×16, 32×32, 64×64, or 128×128 pixels of the size of the extendedmacro-block. Further, the decoded header information includes the motionparameters for motion compensation and prediction. The motion parametermay include the motion parameter transmitted for each block merged by ablock merging method according to an embodiment. The decoder headerinformation also includes a flag indicating whether the planar mode isactivated and the per-unit prediction mode information having theabove-mentioned asymmetric shape.

The motion compensating unit 737 performs motion compensation, using themotion parameter, on the prediction unit having the same size as theprediction unit encoded based on the decoded header information from thebit stream by the entropy decoding unit 731, thereby generating thepredicted prediction unit. The motion compensating unit 737 performsmotion compensation using the motion parameter transmitted for eachblock merged by the block merging method according to an embodiment,thereby generating the predicted prediction unit.

The intra predicting unit 739 performs intra-prediction encoding using apixel correlation between blocks. The intra predicting unit 739 mayobtain the prediction pixel value of the current prediction unit by theintra-prediction encoding method described in connection with FIGS. 6 to11.

The adder 743 adds the residue provided from the inverse transform unit735 to the predicted prediction unit provided from the motioncompensating unit 737 or the intra predicting unit 739 to reconstructthe image and provides the reside to the frame buffer 741 so that theframe buffer 741 stores the reconstructed image.

FIG. 16 is a flowchart illustrating an image decoding method accordingto an example embodiment of the present invention.

Referring to FIG. 16, the decoding apparatus receives the bit streamfrom the encoding apparatus (step S1601).

Thereafter, the decoding apparatus performs entropy decoding on thereceived bit stream (step S1603). The data decoded by entropy decodingincludes the residue which refers to a difference between the currentprediction unit and the predicted prediction unit. The headerinformation decoded by the entropy decoding may include prediction unitinformation, motion parameters for motion compensation and prediction, aflag indicating whether planar prediction mode is activated, andasymmetric-type per-prediction unit prediction mode information. Theprediction unit information may include prediction unit sizeinformation.

Here, in the case that, instead of performing encoding and decodingusing the extended macro-block and the size of the extended macro-block,the above-mentioned recursive coding unit CU is used for encoding anddecoding, the prediction unit PU information may include the sizes ofthe maximum coding unit LCU and minimum coding unit SCU, the maximumpermissible level or level depth, and flag information.

A decoding controller (not shown) may receive from the encodingapparatus the prediction unit PU size information applied in theencoding apparatus and may perform to-be-described motion compensationdecoding, intra-prediction encoding, inverse transform, or inversequantization according to the size of the prediction unit PU applied inthe encoding apparatus.

The decoding apparatus inverse-quantizes and inverse-transforms theentropy-encoded residue (step S1605). The inverse transform may beperformed on the basis of the prediction unit size (for example, 32×32or 64×64 pixels).

The decoding apparatus applies inter prediction or intra predictionmethod to the prediction unit having various shapes, such as theasymmetric or geometrical shapes described in connection with FIGS. 6 to11, thereby generating the predicted prediction unit (step S1607).

The decoder adds the inverse-quantized, inverse-transformed residue tothe prediction unit predicted through the inter or intra prediction,thereby reconstructing the image (step S1609).

Although the example embodiments of the present invention have beendescribed, it will be understood by one of ordinary skill that variousmodifications can be made to the present invention without departingfrom the scope of the invention defined by the appended claims.

What is claimed is:
 1. An apparatus for decoding an image, the apparatuscomprising: an inverse-transform unit configured to reconstruct aresidue by entropy-decoding a received bit stream and by performinginverse quantization and inverse transform on the residue; an intrapredicting unit configured to generate a prediction unit by performingintra-prediction that selectively uses one of a plurality of predictionmodes on a prediction unit which is split; and an adder configured toreconstruct the image by adding the residue to the prediction unit,wherein when a planar intra prediction mode is activated, a predictedpixel value of an internal pixel of a current prediction unit isobtained by performing bilinear interpolation using (i) vertically andhorizontally directional corresponding pixel values in previouslydecoded left side block and upper end block of the current predictionunit, and (ii) vertically and horizontally directional correspondinginternal boundary prediction pixel values in the current predictionunit, wherein the vertically and horizontally directional correspondinginternal boundary prediction pixel values include: a pixel value of afirst pixel which is located on a lowermost boundary of the currentprediction unit and on a same vertical column as the internal pixel, anda pixel value of a second pixel which is located on a rightmost boundaryof the current prediction unit and on a same horizontal row as theinternal pixel.
 2. The apparatus of claim 1, wherein the prediction unitcorresponds to a leaf coding unit when a coding unit is split andreaches a maximum permissible depth.
 3. The apparatus of claim 2,wherein a partition splitting is achieved by an asymmetric partitioningwhen the coding unit is split.
 4. The apparatus of claim 3, wherein theasymmetric partitioning is conducted along a horizontal direction tosplit the prediction unit into a first partition having a size of 64×16and a second partition having a size of 64×48, or into a first partitionhaving a size of 64×48 and a second partition having a size of 64×16. 5.The apparatus of claim 3, wherein the asymmetric partitioning isperformed along a vertical direction to split the prediction unit into afirst partition having a size of 16×64 and a second partition having48×64, or into a first partition having a size of 48×64 and a secondpartition having a size of 16×64.
 6. An apparatus for decoding an image,the apparatus comprising: an inverse-transform unit configured toreconstruct a residue by entropy-decoding a received bit stream and byperforming inverse quantization and inverse transform on the residue; anintra predicting unit configured to generate a prediction unit byperforming intra-prediction that selectively uses one of a plurality ofprediction modes on a prediction unit which is split; and an adderconfigured to reconstruct the image by adding the residue to theprediction unit, wherein when a planar intra prediction mode isactivated, a predicted pixel value of an internal pixel of a currentprediction unit is obtained by performing bilinear interpolation using(i) vertically and horizontally directional corresponding pixel valuesin previously decoded left side block and upper end block of the currentprediction unit, and (ii) vertically and horizontally directionalcorresponding internal boundary prediction pixel values in the currentprediction unit, wherein the vertically and horizontally directionalcorresponding pixel values in the previously decoded left side block andupper end block of the current prediction unit include: a pixel value ofa third pixel which is located on a lowermost boundary of the upper endblock of the current prediction unit and on the same vertical column asthe internal pixel, and a pixel value of a fourth pixel which is locatedon a rightmost boundary of the left side block of the current predictionunit and on the same horizontal row as the internal pixel.
 7. Theapparatus of claim 6, wherein the prediction unit corresponds to a leafcoding unit when a coding unit is split and reaches a maximumpermissible depth.
 8. The apparatus of claim 7, wherein a partitionsplitting is achieved by an asymmetric partitioning when the coding unitis split.
 9. The apparatus of claim 8, wherein the asymmetricpartitioning is conducted along a horizontal direction to split theprediction unit into a first partition having a size of 64×16 and asecond partition having a size of 64×48, or into a first partitionhaving a size of 64×48 and a second partition having a size of 64×16.10. The apparatus of claim 8, wherein the asymmetric partitioning isperformed along a vertical direction to split the prediction unit into afirst partition having a size of 16×64 and a second partition having48×64, or into a first partition having a size of 48×64 and a secondpartition having a size of 16×64.